An imaging method known as the “magnetic tagging method” has been used in recent years to visualize organs in motion, such as the heart, and blood flow using a magnetic resonance diagnosis apparatus (hereinafter called an “MRI apparatus”). This method transmits a radio frequency magnetic field to a part of regions (ordinarily a belt-like or linear region) of an imaging region of an object and lets it get into magnetic saturation so that magnetic resonance signals (hereinafter called “MR signals”) are generated from the belt-like or linear region, then applies a radio frequency magnetic field, gradient magnetic fields, etc, to the imaging region and performs imaging.
Incidentally, the technique of applying the radio frequency magnetic field to a part of the imaging region prior to imaging and bringing the part of the regions into magnetic saturation will be hereinafter called “magnetic tagging”.
The MR signals are not generated or are generated only weakly during imaging in the region that is magnetically tagged and this region is displayed as non-signals or low signals on the image that is later re-constructed. When the region magnetically tagged is a region having less motion, display of the non-signal or the low signal is made as such in the belt-like or linear form, but is displayed in deviation on the image when the region magnetically tagged is a region having motion. This deviation varies depending on a moving distance during the period from magnetic tagging to imaging. Therefore, when magnetic tagging is executed for a region having fast motion, the deviation on the image becomes great, the motion can be visualized and the moving distance can be calculated, too.
Magnetic tagging of this kind is described in JP-A-1-47912, L. Axel et al “Radiology”, Vol. 171, p. 841-845(1989) and W. Kerwinet al “Journal of Magnetic Resonance” Vol. 142, p.313-322 (2000).
However, these prior art technologies two-dimensionally perform magnetic tagging and it is therefore difficult to visualize three-dimensional motion of the organs and to conduct quantitative measurement such as calculation of the moving distance.
Importance of magnetic tagging in three-dimensional regions will be described. Contraction and dilatation of the heart, for example, are performed while each tissue of the heart moves in a three-dimensional space but not on a two-dimensional plane. Because each tissue of the heart thus exhibits three-dimensional motion, the heart exhibits contraction and dilatation with twist as a whole.
To visualize such three-dimensional motion or to quantitatively handle the motion, magnetic tagging of the three-dimensional region is of utmost importance. This also holds true not only for motion of the heart but also for other organs and blood.
It is therefore an object of the invention to provide an MRI apparatus that can solve the problems described above and can more flexibly observe the motion of the organs and the blood.